Soil conservation at Higher Level: Different examples from SL: the Loess Plateau, Burkina Faso's stone lines, China's Three-North Shelterbelt, Mongolia's grasslands and Iowa's cover crops. At HL, weigh each strategy by its costs and benefits (HL.b) and who should pay (HL.c).
Practise this as you read
- Outline a strategy: name it and say how it helps.
- Evaluate a strategy for a named place.
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Soil takes centuries to form, and years to lose: Soil forms at only a few millimetres a century, but bare, overworked fields can lose it in a few storms. Soil conservation keeps soil in place and fertile, and prevention is cheaper than repair.
Stop erosion
- Water: terraces, contour ploughing, bunds, drainage, cover crops.
- Wind: tree and hedge windbreaks, cover crops.
Keep it fertile
- Soil conditioners: lime, compost, manure, green manure.
Farm it gently
- Avoid marginal land, overgrazing and overcropping.
- Strip cultivation, mixed cropping, crop rotation, reduced tillage, agroforestry, lighter machines.
The points to remember
- Environmental benefits: less erosion, cleaner rivers, more soil carbon and wildlife.
- Economic benefits: higher, steadier yields; less spent on fertilizer.
- Sociocultural benefits: food security, farms passed on, fewer people forced to move.
Example (HL): the Loess Plateau, China. Centuries of farming and grazing had left steep, gullied slopes that sent huge loads of soil into the Yellow River. From 1994 a project built terraces, banned free grazing and planted trees and grass on the steepest land. Erosion fell sharply and more than 2.5 million people's incomes rose.
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Rain loosens soil and runoff carries it downhill. Every water technique works by slowing the water, helping it soak in, or covering the soil.
The points to remember
- Terracing: flat steps on a slope slow runoff and let water soak in.
- Contour ploughing: furrows run across the slope, each one catching the water.
- Bunds and stone lines: low walls of earth or stones along the contour trap water and soil.
- Cover crops and mulch: plants or crop waste shield the soil from raindrops.
- Buffer strips of plants by streams catch soil before it reaches the water.
- Drainage and drip irrigation: less water running over the surface.
Remember it as: Slow it, sink it, cover it.
Example (HL): stone lines and zai in Burkina Faso. Farmers in Yatenga lay lines of stones along the contours and dig zai pits. Runoff slows at each stone line and soaks in, and land that had been bare and crusted grows grain again.
Name it AND say how it works: 'Terracing' alone does not score in an outline. 'Terracing makes flat steps on a hillside, which slows runoff' does.
Wind lifts dry, loose, bare soil, mostly on flat, open land. The answer is to slow the wind and keep the soil covered.
The points to remember
- Windbreaks (shelterbelts): rows of trees or hedges slow the wind for about 10-20 tree heights downwind.
- Cover crops and stubble: roots and stalks hold the soil after harvest.
- Strip cultivation: strips of crop between strips of grass, so no wide bare field.
- Keep soil moist and rich in organic matter, so it clumps and does not blow.
Example (HL): China's Three-North Shelterbelt. Since 1978 China has planted billions of trees in a belt across its dry north to slow the wind and stop the deserts spreading. Dust storms have fallen in some areas, but in the driest places many planted trees died for lack of water.
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Some soils erode or fail because they are poor, acidic or worn out. Soil conditioners put that right.
The points to remember
- Lime raises the pH of acidic soils, so nutrients become available again.
- Compost and manure add organic matter: better structure, water-holding and soil life.
- Green manure: a crop such as clover is ploughed back in, adding organic matter and nitrogen.
- Gypsum improves the structure of salty, sodic soils.
- Use organic fertilizer rather than synthetic, which can leave salt residues.
Crop rotation also keeps soil fertile: a different crop is grown in the field each year.
Crop rotation: four benefits
- Different crops use different nutrients, so none is used up.
- It breaks pest and disease cycles: pests of one crop cannot build up.
- Legumes in the rotation add nitrogen.
- Different root depths improve soil structure.
Example (HL): lime in Western Australia. Many of the wheatbelt's sandy soils have become acidic after decades of cropping and fertilizer. Farmers now spread lime on millions of hectares, which raises the pH so wheat roots grow deeper and yields recover.
How the land is worked matters as much as what is added. Less disturbance means more soil stays put.
The points to remember
- Reduced or no tillage: seeds are drilled into last year's crop residue, so the soil is never bare.
- Lighter machines, used less often, avoid compaction, so water soaks in.
- Avoid overgrazing: fewer animals, fencing and rotational grazing let grass recover.
- Avoid overcropping and farming marginal land (steep, dry or thin soils).
- Biological pest control and IPM avoid pesticides that kill soil organisms.
Example (HL): Mongolia's grasslands. After 1990 the number of herd animals rose from about 25 million to about 70 million, and much of the steppe was overgrazed. Herder groups now agree grazing rotations and rest pastures, so the grass and its soil can recover.
Link it to the soil: Water saving or pest control alone does not answer a soil question. Say what it does for the soil: 'drip irrigation stops runoff washing soil away'.
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Growing several crops, or trees and crops, together keeps the ground covered and spreads the risk.
The points to remember
- Mixed cropping / intercropping: two or more crops in one field at the same time.
- Benefits: legumes fix nitrogen; more plant waste adds nutrients; less erosion.
- Farmers gain: more crops per hectare, less risk of total crop failure, fewer pests, varied income.
- Agroforestry: tree roots hold soil, the canopy breaks the rain, leaf litter adds organic matter.
- Unlike slash-and-burn, agroforestry keeps the land in use for good with no burning.
Remember it as: Many plants, one field: cover, nitrogen, insurance.
Example (HL): shade coffee in Costa Rica. Many farmers grow coffee under Erythrina and banana plants. The trees drop leaves that feed the soil, hold the steep slopes together, shelter birds, and give timber and fruit to sell.
When soil is already damaged, it can be restored, but slowly and at a cost. That is why prevention comes first.
The points to remember
- Add organic matter: compost, manure, biochar.
- Lime for acidic soils; gypsum for sodic soils.
- Replant: trees and grass stabilize the soil and add organic matter.
- Rest the land, fenced from animals, so plants return.
- Sustainability means meeting today's needs without harming the soil for the future.
A bare fallow can harm soil: Leave a field bare and unplanted and roots no longer hold it: wind and rain erode it, rain leaches minerals, and soil life declines. A fallow needs a cover.
Example (HL): exclosures in Tigray, Ethiopia. Communities fence off degraded hillsides from animals and woodcutting, and build stone terraces below them. Within ten years grass, shrubs and soil return, but families must find grazing and firewood elsewhere.
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To evaluate a strategy, name it, give its advantages and its disadvantages, then judge.
Advantages to look for
- Less soil lost to wind or water.
- Keeps nutrients and water in the soil.
- Higher, steadier yields and incomes.
Disadvantages to look for
- Cost of building or buying (walls, trees, machines).
- Labour and knowledge needed.
- Land lost to walls, hedges or strips; lower yields at first.
Example (HL): cover crops in Iowa, USA. Cereal rye sown after the maize harvest holds the soil over winter and cuts nitrate losses. But seed and sowing cost money, the rye can slow the next crop, and only a small share of Iowa's fields use it, even with state payments.
The points to remember
- Strategy named first.
- Up to two advantages and up to two disadvantages.
- A conclusion that weighs them, using the case.
How this comes up: Paper 1 gives a fact file on a farming region and asks you to evaluate one strategy to make it more sustainable [4].
The fact file describes coffee farming in Vietnam's Central Highlands.
Evaluate one strategy coffee farmers could adopt to make their farming more sustainable.
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